This invention relates to a thin and high-output stepping motor adapted to be used in a floppy disk control mechanism and an industrial robot for the purpose of determining positions at a high precision.
Heretofore, a stepping motor of the above described type having an axial gap has been proposed (refer to Japanese Patent Application No. 11559/1984 invented by Yasuyuki Kojima and filed on Jan. 24, 1984). Although the construction of the disclosed stepping motor is comparatively simple, the stator core thereof must be made into a solid form, thus increasing iron loss and reducing efficiency when the stepping motor is driven from a polyphase high-frequency power source. Furthermore, since the utility of magnetic fluxes is reduced at a high-speed operation, the size of the magnet used in the stepping motor increases, and the production of a small size, thin, and high-power stepping motor is thereby made difficult.
A stepping motor having a radial gap has also been proposed (refer to, for instance, U.S. Pat. No. 3,866,104 entitled "Five phase stepping motor", invented by Gunter Heine). However, a large number of salient poles and slots are formed around the surfaces of the rotor and the stator, and therefore particularly in the case of a stepping motor having a minute increment, the number of the production steps has been inevitably increased. In addition, since the rotor of this type stepping motor is made of permanent magnets, the required amount of the permanent magnets increases, thus increasing the production cost of the stepping motor.